1. Field of the Invention
The present invention relates to image scanning apparatuses, image processing apparatuses, image producing apparatuses, and image processing methods. In particular, the present invention relates to an image scanning apparatus, an image processing apparatus, an image producing apparatus, and an image processing method for generating high-resolution color images.
2. Description of the Related Art
Conventionally, in image scanning apparatuses, such as scanners, and image producing apparatuses, such as copiers, a 3-line CCD sensor constituted by three line sensors for red, green, and blue has typically been used as a color-image scanning sensor.
The 3-line CCD sensor has a configuration in which three 1-dimensional line sensors, which have red, green, and blue color filters on the respective light receiving surfaces, are arranged. Thus, the 3-line CCD sensor cannot simultaneously scan the same spot on a document with all the line sensors. Accordingly, with respect to position misalignment in a document scanning direction, a memory circuit including line memories or the like is used to align image signal positions scanned by the line sensors.
In recent years, a 4-line CCD sensor constituted by 4 line sensors has also been commercially available. The 4-line CCD sensor includes a monochrome scanning line sensor that does not have a color filter on the light receiving surface, in addition to the 3-line CCD sensor for scanning color images.
Patent Document 1 (JP-A 2003-87556) discloses an image scanning apparatus using a 4-line CCD sensor, i.e., a monochrome scanning line sensor and a three color scanning line sensors. In the disclosed technology, the pixel light-receiving area of the monochrome-scanning line sensor and the pixel light-receiving area of each color-scanning line sensor are different from each other, so that a monochrome document is scanned with a high resolution and a color document is scanned with a high sensitivity. Patent Document 1 further discloses a technology for enhancing the resolution of an image, obtained by the color-scanning line sensors, by using a high-resolution luminance signal obtained by the monochrome-scanning line sensor.
A typical image-scanning apparatus scans an image by causing a motor to mechanically drive line sensors. Thus, motor speed-irregularity, vibration, and so on often affect the image. In particular, with color line CCD sensors, since the line CCD sensors for red, green, and blue are physically spaced apart from each other, the occurrence of motor speed-irregularity and/or vibration can cause color misalignment. Even with, for example, the image scanning apparatus using the 4-line CCD sensor disclosed in Patent Document 1, the color misalignment can similarly occur.